A heat capacity laser was described for the first time in U.S. Pat. No. 5,526,372 A. The heat capacity laser has a solid lasing medium, a pumping source, and an optical cavity. The specificity of the heat capacity laser resides in the fact that it is not cooled in lasing mode. On the contrary, the heat released is stored in the lasing medium. As a result, the duration of the lasing mode is a function of the maximum amount of thermal energy storable in the lasing medium. The maximum amount of thermal energy that can be stored is a function of the mass of the lasing medium, the specific heat of the lasing medium material, and the difference between the starting temperature and the final temperature. U.S. Pat. No. 5,526,372 A deals in particular with the temperature distribution in the lasing medium. The text of this patent indicates that it is extremely advantageous for the temperature to be higher outside than inside the lasing medium. In proportion to the temperature level, a greater expansion is observed outside the lasing medium. As a result, this means that the lasing medium will undergo greater compression stresses outside—a phenomenon to be favored. In terms of its mechanical characteristics, the lasing medium can be compared to glass: it withstands high compression stresses but low tensile stresses. If there are defects on the outer surface, the outside compression stresses do not bring about fissure propagation. Related to the duration of the lasing mode referred to above, the compression stresses in the outer envelope are able to raise the maximum temperature allowable by the lasing medium. As a result, the amount of heat stored is increased. The operating time in lasing mode is thus prolonged.
U.S. Pat. No. 6,862,308 B2 describes another heat capacity laser. For this heat capacity laser, a barrel with several lasing media is used, as well as a loading and unloading device. When a lasing medium has reached is maximum temperature, it is unloaded and cooled. At the same time, it is replaced by another cooled lasing medium coming from the barrel. In this patent, the reader's attention is drawn to the fact that the temperature is higher on the outside of the lasing medium, and to the tensile stresses under pressure generated by this fact, so that higher temperatures can be tolerated.